Cerebral Cortical Mechanisms in Somesthesis. The long-term objective of this research is to discover the intrinsic operating mechanisms of the primate cerebral cortex, particularly those leading to sensation and perception, and to sensory-motor trans- formations. Experiments will be made in waking monkeys as they execute tasks in the somesthetic mode of flutter-vibration, detecting and discriminating between mechanical sinusoids of differing frequencies and amplitudes delivered to the glabrous skin of their hands. The electrical signs of the activity of cortical neurons will be recorded with multiple microelectrodes (n = 7), both by acute insertion in successive daily experiments and after chronic implantation. The first specific aim is to record simultaneously the activity of neurons in the different layers of the primary somatic sensory area 3b of the postcentral gyrus, to discover what transforms are imposed by the intra-columnar proces- sing chains upon the evoked thalamocortical input, and how that transformation may differ along chains leading to different output projection lines; e.g., those that originate in the supra- and infra-granular layers. The second specific aim is to record simultaneously in different layers of areas 1, 2, and 5, to discover how the primary transformations of the dynamically driven cortical activity is further modified along the multistaged cortical system leading from primary sensory to homotypical cortical areas and, it is thought, to sensation and perception. The third specific aim is to study the trans-callosal sensory-motor transform in animals trained to make differential motor responses with one hand after making sen- sory discriminations between stimuli delivered to the other hand. Multiple microelectrode recordings will be made in areas 2, 5 and 4 of the hemisphere ipsilateral to the hand receiving sensory input, and contralateral to the hand making differential motor responses. The fourth specific aim is to study the primary sensory areas, in the manner described above, after chronic implantation of many microelectrodes, to discover what changes occur during long periods of daily sensory training, and whether the spatial, modality, or dynamic response characteristics of cortical neurons can be modified by changes in sensory experience.